A $90 upgrade on a $299 drone is a significant percentage. .
A few points:
-The $299 price for the Solo is out of the ordinary - a result of 3DR's business fortunes, not a reasonable price for the platform. It really is an $800 to $1000 drone selling on clearance for $299. When they're gone, they're gone, and other drones still have yet to match Solo's capabilities. Personally, I want to keep mine, and keep them undamaged, as long as possible, and $85 is a small amount of money to do just that. If someone gave you a new car for free, would you not bother changing the oil because the cost of doing so would be more than your investment in the car?
-The new GPS improves both the time-to-fly, as well as the accuracy of the smartshots. As a camera platform, this is virtually the whole point, and $85 is, again, a small amount of money for such improvements.
-When your Solo takes to the air with your ~$400 camera, it's not just a $299 drone anymore. Since GoPros cost more than new Solos at this point, I definitely don't want to have to replace the camera on top of the drone.
-Solo is a heavy chunk of metal and plastic flying through the air, and could cause significant injury if it were to fly away and out of control. $85 is a tiny cost to reduce the chance of this.
It's also for all those reasons I wouldn't cheap out by buying a highly likely counterfeit GPS from some unknown Chinese eBay seller for $20.
I don't mean to criticize, but it amazes me how little people really think things through.